Nonlinear refraction in CH$_3$NH$_3$PbBr$_3$ single crystals

We measure both nonlinear absorption and nonlinear refraction in a CH3NH3PbBr3 single crystal using the Z-scan technique with femtosecond laser pulses. At 1000 nm, we obtain values of 5.2 cm/GW and +9.5 10(-14 )cm(2)/W for nonlinear absorption and nonlinear refraction, respectively. The sign and magnitude of the observed refractive nonlinearity are reproduced well by the two-band model. Our results suggest that the large nonlinear refractive index measured in perovskite nanostructures cannot be explained by an intrinsically high bound-electronic nonlinear refractive index in this emerging material class but is possibly caused by free carriers or quantum confinement effects. (C) 2020 Optical Society of America